1. Field of the Invention
The present invention relates generally to mobile stations operating in wireless communication networks, and more particularly to methods and apparatus for reducing signal interference in a wireless receiver having a low noise amplifier (LNA) with use of a detected signal-to-interference (S/I) ratio.
2. Description of the Related Art
A wireless communication device, such as a mobile station operating in a wireless communication network, may provide for both voice telephony and packet data communications. A mobile station may, for example, be compatible with 3rd Generation (3G) communication standards (such as IS-2000 Release 0) and utilize Global System for Mobile Communications (GSM), Time Division Multiple Access (TDMA), or Code Division Multiple Access (CDMA) wireless network technologies.
All of these communication standards utilize radio frequency (RF) signal detection techniques. In an RF receiver, internal thermal noise is sometimes the predominate source of interference to the desired signal. In this case, a lower noise figure of the receiver is appropriate and will lead to improved receiver sensitivity. At other times, external in-band interference (including external in-band noise) is the major source of interference as the out-of-band portion of the interference is insignificant to cause distortion. This in case, a higher in-band dynamic range of the receiver is appropriate and required for good performance. The in-band dynamic range of the receiver is usually measured by the in-band 3rd order interception point (i.e. “in-band IP3”). At other times, the out-of-band interference is the primary source of interference, producing distortions in the in-band spectrum through non-linearity of the receiver. In this case, a higher out-of-band dynamic range of the receiver is needed to improve performance. The out-of-band dynamic range is usually measured by the out-of-band 3rd order interception point (i.e. “out-of-band IP3”).
The higher dynamic range requirements described above are often in conflict with the lower noise figure requirement. The former prefers a lower front end gain, while the latter needs a higher front end gain. A front end that is designed to be good for both scenarios would be expensive in cost. For a lower cost solution, some receiver designs include a variable front end stage. In particular, a low noise amplifier (LNA) of the front end may have an adjustable gain G which is controlled by a feedback mechanism. In general, the gain G of the LNA is adjusted dynamically in response to the feedback mechanism in order to trade off the noise figure with the dynamic range of the LNA when necessary. The feedback mechanism includes a level detector having an input signal which may be provided from one of a few different sources. Where the input signal is taken from analog sources of the receiver, the level detector can advantageously detect both in-band and out-of-band contents of the signal/interference/distortion. However, the disadvantage is one of relatively higher cost and lower accuracy inherent in today's analog signal processing. When the level detector is part of a digital signal processor (DSP), the advantage is one of relatively lower cost and higher accuracy inherent in today's digital signal processing. However, the disadvantage is that the level detector within the DSP can only sense in-band contents of the signal/interference/distortion.
Accordingly, what are needed are methods and apparatus for reducing signal interference in a wireless receiver so as to overcome the deficiencies in the prior art.